1. Field of the Invention
The present invention relates to a method for the preparation of certain alkyl halides by the reaction between carbon monoxide and hydrogen (synthesis gas) and a hydrohalide in the presence of a novel catalyst under mild conditions.
2. Prior Art
Until recently, two principal methods were employed industrially for the synthesis of methyl halides. One method involves the chlorination of methane and the other relies on the reaction between methanol and a hydrogen halide. The latter process is the most widely employed and accounts for most of the methyl chloride production in the world. This method produces methyl halide as the sole product of reaction whereas the halogenation of methane typically yields mixtures of methyl halide, methylene halide, haloform and carbon tetrahalide.
Both of these procedures, however, require the utilization of relatively high temperatures and, typically, high pressures, to achieve acceptable yields. These rigorous reaction condition requirements necessitate the use of expensive equipment and not infrequent shutdowns for repair and replacement thereof due to the deleterious effects of hydrogen halide thereon at elevated temperatures. Such necessary demands on the system used for synthesis of the methyl halides contribute to the high cost of methyl halide in the marketplace.
U.S. Pat. No. 4,041,087 describes a method for the preparation of halogenated hydrocarbons, including methyl halides, by reacting carbon monoxide, hydrogen and a source of halogen in the presence of a particular catalyst at temperatures from 200.degree. to 1000.degree. C., preferably 200.degree. -700.degree. C. and at pressures from 0.1 to 500 atm, most preferably 1 -10 atm. In the examples of preferred embodiments set forth in the patent, temperatures of 270.degree. C. and above are employed. The catalyst is described as one of several specific Group VIII metals or alloys (rhenium, platinum-iridium and platinum-rhenium) in combination with an acidic inorganic oxide material.
Although the patented method represents a new approach to the preparation of halogenated hydrocarbons, it also requires the utilization of substantially the same rigorous conditions employed in typical prior art methods. As a result, the costs of halogenated hydrocarbons produced according to the patented method remain relatively high.
Recently, a method was patented (U.S. Pat. No. 4,538,011) for preparing methyl halide or mixtures of methyl halide and ethyl halide by reacting CO, H.sub.2 and HX at a temperature below 200.degree. C. in the presence of a catalyst comprising a metal carbonyl complex capable of oxidatively adding hydrogen or HX having the formula M.sub.n (CO).sub.m wherein M is a transition metal, n and m may be the same or different and are integers having a value of at least 1, in association with (1) at least one Lewis or Bronsted acid capable of coordinating the oxygen atom of said carbonyl moiety and (2) at least one Lewis base other than CO attached to the metal of the metal carbonyl complex having the formula Z.sub.y [M.sub.n -(CO).sub.m y-]wherein M, n and m have the meanings set forth above, y is an integer having a value of at least 1 and Z is a cation or a cationic support ionically bonded to or in association with the transition metal anion.
The patented method produces large amounts of desired product at temperatures between 20.degree. and 100.degree. C. thereby greatly reducing the overall cost of the apparatus and systems required for handling the reactants and conducting the reaction and lessening the cost of the product.
The present invention is an improvement over that described in U.S. Pat. No. 4,538,011.